The present invention relates to a method and equipment for the transfer of workpieces which are processed in at least one first group of work stations and in at least one second group of work stations of a production line, wherein a first transfer device moves workpiece carriers with the workpieces from work station to work station of the first group, and a second transfer device moves workpiece carriers with the workpieces from work station to work station of the second group and wherein the first transfer device hands over the workpiece carriers to an interchange device and the interchange device feeds the workpiece carriers to the second transfer device.
A transfer device in which workpieces are transported by means of workpiece carriers from work station to work station of a production line has become known from laid-open specification DE 198 26 627 A1. The work stations are arranged in a line and provided with assembly devices and/or processing devices. A first group of work stations executes time-intensive work procedures and a second group of work stations executes less time-intensive work procedures, wherein the first group is disposed upstream of the second group production with reference to the direction of workflow. A first transfer device moves the workpiece carriers from work station to work station of the first group. A second transfer device moves the workpiece carriers from work station to work station of the second group. An interchange device is connected between the two transfer devices, wherein the first transfer device hands over the workpiece carriers to the interchange device and the interchange device feeds the workpiece carriers to the second transfer device. The workpiece carriers pass from the first transfer device to a transport belt of the interchange device, wherein the transport belt pre-positions the workpiece carriers in that the workpiece carriers are moved up to a retaining element. At the entry side the second transfer device has a coupling section which, by means of a stroke movement, grips a workpiece carrier at a toothed profile at its base side and passes it on to a belt drive. The stroke movement of the coupling section is derived from a control shaft for the work stations of the second group.
A disadvantage of the known equipment resides in the fact that the onward movement of the workpiece carriers within the interchange device is effected by means of a frictional force between the workpiece carriers and a flat belt. If the frictional force falls below the requisite traction force of the workpiece carrier, the workpiece carrier is left standing in uncontrolled manner. A greater mass of the workpiece carrier can increase the tractive force. Heavier workpiece carriers, however, cause greater wear and require lower transport speeds.
The present invention, as characterised in claims 1 and 4, meets the object of avoiding the disadvantages of the known equipment and of advancing the workpiece carriers independently of the frictional force between the workpiece carrier and the transport belt. In accordance therewith, the present invention provides independent drives for the transfer devices and the interchange device. The motion of the interchange device can be synchronized with the motion of the transfer devices to maintain proper work flow. Means may be provided on the transfer devices, interchange device, and workpiece holders to insure a positive, non-slip interconnection. In a preferred embodiment each of the transfer devices and the interchange device are independently driven, and incorporate cogged belts which engage complementary-profiled workpiece holders.
The advantages achieved by the invention are essentially to be seen in that the workpiece carriers are transported within the entire production line in a mechanically positively coupled manner. The production line can thereby be optimised in length and the processing plant can thus be constructed to be shorter and requires less space. The interchange device can operate with a smallest possible pitch, or transport workpiece carrier against workpiece carrier, and subsequently pass them over to a transport unit at a different pitch. Moreover, the equipment for the transfer of the workpiece carriers can be constructed substantially more simply in mechanical terms, which in turn has a favourable effect on the production costs of the processing plant. In addition, the equipment manages with few wear parts, which increases reliability and reduces maintenance expenditure.